Update cloud package.

impl/cloud/context.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package cloud
 
 import (
-        "google.golang.org/cloud/datastore"
+        "cloud.google.com/go/datastore"
 
         "golang.org/x/net/context"
 )
 
 // Use installs the cloud services implementation into the supplied Context.
 //
 // This includes:
 //      - github.com/luci/gae/service/info
 //      - github.com/luci/gae/service/datastore
 //
 // This is built around the ability to use cloud datastore.
 func Use(c context.Context, client *datastore.Client) context.Context {
         return UseDS(useInfo(c), client)
 }
 
 // UseDS installs the cloud datastore implementation into the supplied Context.
 func UseDS(c context.Context, client *datastore.Client) context.Context {
         cds := cloudDatastore{
                 client: client,
         }
         return cds.use(c)
 }